Adding substances to living cells is significant for biological research as well as for gene technology. Various methods already exist for performing this work. The substance which is to be brought into the cells can first be placed in the medium surrounding the cells. The cell membrane must be penetrated so that the substance can get into the cells. This can take place by means of non-directed mechanical, electrical or chemical stimuli or by means of a laser beam which is focused on the cell.
All these methods have the disadvantage that the substance which is to be brought into the cell remains for the most part in the surrounding medium. Above all, it is not possible with the above-mentioned methods to deliver the substances only into the nucleus of a cell. For this reason, methods have been developed by means of which the substance is injected directly into the individual cells or cell nuclei with the aid of a glass capillary which is drawn out to a fine point at one end.
The publication entitled "Workplace for Microinjection into Living Cells" published by Carl Zeiss in the Federal Republic of Germany under publication number W41-131-e(XI-86) describes a system based on an inverted microscope. The inverted microscope has a stage on which a glass capillary is attached via a micromanipulator. The glass capillary is positioned so that it is inclined with respect to the optical axis of the microscope. The capillary can be purposefully moved in three axes in the culture vessel with the aid of the micromanipulator with the culture vessel being disposed on the stage of the microscope. The following individual steps are carried out for injection into the cells observed visually under the microscope: first the point of the capillary must be coarsely brought into the image field of the objective. Thereafter, the point of the capillary is positioned over the cell of interest by means of a movement of the micromanipulator (x, y). Finally, by means of a movement in the z-direction (that is, parallel to the optical axis of the microscope), the capillary point is brought into the cell and the injector is actuated and, after an adequate quantity of substance has been brought into the cell, the capillary is again lifted. In these steps, the injection does not occur in the direction of the axis of the capillary.
The above-described method is a purely manual method and requires several individual steps which are carried out precisely one after the other and for which some experience is necessary in order to correctly hit the cells and especially not to lower the capillary too far and thereby break the same. Furthermore, the penetration into the cells is not in the axial direction of the capillary so that the cell membrane is relatively seriously injured by means of the injection operation.
Another injection system is disclosed in the German patent publication No. DE-OS 35 11 700 which includes a capillary coupled to the focus drive of an inverted microscope and which is arranged in a vertical direction. In this system, the capillary must be first adjusted in the z-direction so that a movement of the capillary within the depth of field range of the microscope leads to a penetration into the cell. Thereafter, the cell into which the injection is to be made is driven with the aid of the mechanical stage beneath the point of the capillary which is only imprecisely recognizable. Thereafter, the actual injection operation is carried out in that the capillary is lowered with the aid of the focus drive and penetrates into the cell in the axial direction. After the injection is completed, the capillary is again lifted.
In this system, the danger is especially acute that the point of the capillary will break off or at least will become blocked when the point of the capillary reaches the base of the vessel since the capillary point comes into contact engagement with the base of the vessel in a direction perpendicular thereto. Furthermore, one easily loses the overview as to which cells have already been injected since the stage of the microscope is displaced with each injection whereby the image field continuously changes.
All this has as a consequence that with the known manual systems for cell injection, no more than approximately 300 cells can be injected in an hour, even by experienced personnel.
Furthermore, microbiological methods are known which provide for the drawing off of liquid from cells by suction or the drawing off by suction of entire cells from the cell culture. For this work, the capillary is used to penetrate into the cell or the capillary is positioned on the cell to be withdrawn by suction. In principle, with this method the same working steps are utilized as described above with respect to the example of the injection and the same limitations are present with respect to the speed with which the work can be performed.